Many hardwired communications systems use plug and jack connectors to connect a communications cable to another communications cable or to a piece of equipment such as a computer, printer, server, switch or patch panel. By way of example, high speed communications systems routinely use such plug and jack connectors to connect computers, printers and other devices to local area networks and/or to external networks such as the Internet. FIG. 1 depicts a highly simplified example of such a hardwired high speed communications system that illustrates how plug and jack connectors may be used to interconnect a computer 11 to, for example, a network server 20.
As shown in FIG. 1, the computer 11 is connected by a cable 12 to a communications jack 15 that is mounted in a wall plate 19. The cable 12 is a patch cord that includes a communications plug 13, 14 at each end thereof. Typically, the cable 12 includes eight insulated conductors. As shown in FIG. 1, plug 14 is inserted into an opening or “plug aperture” 16 in the front side of the communications jack 15 so that the contacts or “plug blades” of communications plug 14 mate with respective contacts of the communications jack 15. If the cable 12 includes eight conductors, the communications plug 14 and the communications jack 15 will typically each have eight contacts. The communications jack 15 includes a wire connection assembly 17 at the back end thereof that receives a plurality of conductors (e.g., eight) from a second cable 18 that are individually pressed into slots in the wire connection assembly 17 to establish mechanical and electrical connections between each conductor of the second cable 18 and a respective one of a plurality of conductive paths through the communications jack 15. The other end of the second cable 18 is connected to a network server 20 which may be located, for example, in a telecommunications closet of a commercial office building. Communications plug 13 similarly is inserted into the plug aperture of a second communications jack (not pictured in FIG. 1) that is provided in the back of the computer 11. Thus, the patch cord 12, the cable 18 and the communications jack 15 provide a plurality of electrical paths between the computer 11 and the network server 20. These electrical paths may be used to communicate electrical information signals between the computer 11 and the network server 20.
When signals are transmitted over a conductor (e.g., an insulated copper wire) in a communications cable, electrical noise from external sources may be picked up by the conductor, degrading the quality of the signal. In order to counteract such noise sources, the information signals in the above-described communications systems are typically transmitted between devices over a pair of conductors (hereinafter a “differential pair” or simply a “pair”) rather than over a single conductor. The two conductors of each differential pair are twisted tightly together in the communications cables and patch cords so that the eight conductors are arranged as four twisted differential pairs of conductors. The signals transmitted on each conductor of a differential pair have equal magnitudes, but opposite phases, and the information signal is embedded as the voltage difference between the signals carried on the two conductors of the pair. When the signal is transmitted over a twisted differential pair of conductors, each conductor in the differential pair often picks up approximately the same amount of noise from these external sources. Because approximately an equal amount of noise is added to the signals carried by both conductors of the twisted differential pair, the information signal is typically not disturbed, as the information signal is extracted by taking the difference of the signals carried on the two conductors of the differential pair, and this subtraction process may mostly cancel out the noise signal.
Referring again to FIG. 1, it can be seen that a series of plugs, jacks and cable segments connect the computer 11 to the server 20. Each plug, jack and cable segment includes four differential pairs, and thus a total of four differential transmission lines are provided between the computer 11 and the server 20 that may be used to carry two way communications therebetween (e.g., two of the differential pairs may be used to carry signals from the computer 11 to the server 20, while the other two may be used to carry signals from the server 20 to the computer 11). Unfortunately, the proximities of the conductors and contacting structures within each plug-jack connection (e.g., where plug 14 mates with jack 15) can produce capacitive and/or inductive couplings. These capacitive and inductive couplings in the connectors (and similar couplings that may arise in the cabling) give rise to another type of noise that is known as “crosstalk.”
In particular, “crosstalk” refers to unwanted signal energy that is capacitively and/or inductively coupled onto the conductors of a first “victim” differential pair from a signal that is transmitted over a second “disturbing” differential pair. The induced crosstalk may include both near-end crosstalk (NEXT), which is the crosstalk measured at an input location corresponding to a source at the same location (i.e., crosstalk whose induced voltage signal travels in an opposite direction to that of an originating, disturbing signal in a different path), and far-end crosstalk (FEXT), which is the crosstalk measured at the output location corresponding to a source at the input location (i.e., crosstalk whose signal travels in the same direction as the disturbing signal in the different path). Both types of crosstalk comprise an undesirable noise signal that interferes with the information signal that is transmitted over the victim differential pair.
While methods are available that can significantly reduce the effects of crosstalk within communications cable segments, the communications connector configurations that were adopted years ago—and which still are in effect in order to maintain backwards compatibility—generally did not maintain the arrangement and geometry of the conductors of each differential pair so as to minimize the crosstalk coupling between the differential pairs in the connector hardware. For example, pursuant to the ANSI/TIA-568-C.2 standard approved Aug. 11, 2009 by the Telecommunications Industry Association (also known as the Category 6a standard), in the connection region where the blades of a modular plug mate with the contacts of the modular jack (referred to herein as the “plug-jack mating region”), the eight conductors 1-8 must be aligned in a row, with the eight conductors 1-8 arranged as four differential pairs specified as depicted in FIG. 2. As is apparent from FIG. 2, this arrangement of the eight conductors 1-8 will result in unequal coupling between the differential pairs, and hence both NEXT and FEXT is introduced in each connector in industry standardized communications systems.
As the operating frequencies of communications systems has increased, crosstalk in the plug and jack connectors has became a more significant problem. To address this problem, communications jacks now routinely include compensating crosstalk circuits that introduce compensating crosstalk that was used to cancel much of the “offending” crosstalk that is introduced in the plug jack mating region as a result of the industry-standardized connector configurations. Initially, so-called “single-stage” crosstalk compensation circuits were developed that could cancel the “offending” crosstalk that is generated in a plug jack connector because a first conductor of a first differential pair couples more heavily with a first of the two conductors of a second differential pair than does the second conductor of the first differential pair. Typically, these single-stage crosstalk compensation circuits were implemented by configuring the jack so that the second conductor of the first differential pair would couple with the first of the two conductors of the second differential pair later in the jack to provide a “compensating” crosstalk signal. As the first and second conductors of the differential pair carry equal magnitude, but opposite phase signals, so long as the magnitude of the “compensating” crosstalk signal that is induced in such a fashion is equal to the magnitude of the “offending” crosstalk signal, then the compensating crosstalk signal that is introduced later in the jack may substantially cancel out the offending crosstalk signal.
While the above-described “single-stage” crosstalk compensation circuits were generally effective at cancelling out most of the crosstalk for low frequency signals (e.g., below 100 MHz), as the industry moved to higher frequency signals the phase change between the offending crosstalk signal and the compensating crosstalk signal became more significant such that it became difficult to achieve sufficient crosstalk compensation. Consequently, the use of “multi-stage” crosstalk compensation schemes became common. Such crosstalk schemes are described in U.S. Pat. No. 5,997,358 to Adriaenssens et al., the entire content of which is hereby incorporated herein by reference as if set forth fully herein.
Work is now ongoing in the industry to develop a Category 8 standard that will specify parameters for higher data rate communications plugs, jacks and cable segments that may operate at higher frequencies. For example, the above-referenced ANSI/TIA-568-C.2 Category 6a standard provides for communications at frequencies up to 500 MHz. In contrast, it is anticipated that the Category 8 standard may call for communications at frequencies up to, for example, 2 GHz. Moreover, it is anticipated that Category 8 connectors (e.g., plug and jacks) may be required to exhibit full backwards compatibility so that they may be used with conventional Category 6 or 6a connectors while meeting the component and channel performance requirements set forth in the Category 6 and 6a standards. Special challenges may be involved in providing communications connectors that can meet the Category 8 performance standards over the full anticipated Category 8 frequency range while also providing full backwards compatibility.